N6-methyladenosine-dependent upregulation of lnc-28509 increases apoptosis and suppresses bacterial infection in sea cucumber.

In recent years, lncRNAs (long non-coding RNAs) as well as m6A (N6-methyladenosine) modification have been found to play important roles during pathogens infection induced innate immune response. However, the relationship between the lncRNAs and m6A modification remains unclear. Here, we show that the lncRNA (lnc-28509) from sea cucumber Apostichopus japonicus was significantly induced in response to Vibrio splendidus infection. Knockdown of lnc-28509 inhibits the apoptosis of coelomocytes in sea cucumber and the elimination of Vibrio splendidus. In addition, m6A is highly enriched on lnc-28509 transcripts modified by methyltransferase like 3 (METTL3) upon Vibrio splendidus infection and the METTL3 mediated m6A modification increased lnc-28509 expression through suppressing the decay of lnc-28509. Meanwhile, dual-luciferase reporter assay results revealed that lnc-28509 functions as a miRNA sponge of miR-2012, and miR-2012 inhibits the coelomocytes apoptosis via targeting apoptosis-inducing factor 1 (AIF-1) directly. The results suggested that lnc-28509 regulates apoptosis through sponging miR-2012 and promoting the accumulation of AIF-1. The unique m6A-dependent lncRNA-miRNA interaction can maintain the anti-bacterial role of lnc-28509. Collectively, these data highlight the critical role of m6A modification in the invertebrate lncRNA and reveal a previously unknown mechanism through which lncRNA-dependent cell apoptotic controlled bacterial infection.